Interferometers
MICHELSON INTERFEROMETER
The American physicist Albert Michelson invented the optical interferometer. The incoming beam is split into two beams by the half-silvered mirror. Each sub-beam reflects off of another mirror, which returns it to the half-silvered mirror, where the two sub-beams recombine as shown. One of the reflecting mirrors is movable by a sensitive micrometer device, allowing the path length of the corresponding sub-beam, and hence the phase relationship between the two sub-beams, to be altered. Additional information available at "http://www.physics.nmt.edu/~raymond/classes/ph13xbook/node13.html" [Summary provided by New Mexico Tech]